What is a right hilar lymph node

Lymphatic drainage of the skin

The skin of the thorax achieves lymphatic drainage via a superficial and a deep system.

• The superficial lymphatic vessels converge in the subcutaneous space and take lymph back to the axillary lymph nodes.
• The deep lymphatic system, on the other hand, drain to the intercostal nodes, as well as to the parasternal and diaphragmatic nodes.

Lymphatic drainage of the breast

Another clinically relevant lymphatic pathway associated with the anterior chest wall is that of the breast lymphatics. The breasts, or mammary glands, are anatomically and functionally dichotomous structures associated with reproduction and human sexuality.

Of note, breast lymph channels are avalvular; therefore any occlusion (secondary to tumors) can result in reversal of blood flow. There are numerous periductal and perilobular vessels that parallel the venous tributaries of the breast.

In both males and females, the breast can be divided into quadrants.

• The regions superior to the nipple-areolar complex are the upper quadrants, while those inferior to the complex are the lower quadrants.
• Similarly, the quadrants lateral to the complex are outer quadrants and those medial to it are the inner quadrants.

From this notion, the inner quadrants, and the lower outer quadrant drain primarily to the parasternal and inframammary lymph nodes. The upper outer and part of the lower outer quadrants drain primarily to the axillary nodes. The medial part of each breast also drains to the internal thoracic lymph nodes, which subsequently drains to the superior and inferior epigastric lymph pathways to the groin. Furthermore, the left and right breasts, although symmetrical, have different terminal lymph drainage points. The left breast lymphatics drain via the thoracic duct to the left subclavian vein, while the right breast drains to the right jugulo-subclavian junction. Additionally, lymphatic channels originating from one mammary gland may cross the midline and terminate in nodes associated with the contralateral breast.

Parasternal lymph nodes

The parasternal lymph nodes are a group of four to five nodes residing at the anterior limit of the intercostal space, adjacent to the thoracic arteries.

In addition to draining the breast, they also receive lymph from deep structures of the epigastrium, deeper parts of anterior thoracic wall and the cranial surface of the liver. The efferent vessels of these nodes then anastomose with vessels associated with the tracheobronchial and brachiocephalic nodes to form the bronchomediastinal trunk. This vessel has a variety of terminal points, including in the jugular or subclavian veins, or at the junction of these vessels (jugulo-subclavian junction), the left thoracic duct or the right lymphatic duct.

Diaphragmatic lymph nodes

Additionally, there are lymph nodes located on the thoracic (superior) surface of the diaphragm known as diaphragmatic nodes (also known as superior phrenic nodes). These nodes are further subdivided into anterior, lateral and posterior groups.

• The anterior diaphragmatic group of nodes are comprised of about three nodes posterior to the xiphoid process. There are additional small nodes at the level of the seventh costochondral junction. Afferent lymphatic vessels to these nodes arise from the anterior lymph vessels of the diaphragm; while efferent lymphatic vessels from the same pass to the parasternal nodes.
• The lateral group of thoracic diaphragmatic lymph nodes are further subdivided into left and right groups of two or three nodes. They are adjacent to the point at which the phrenic nerves pierce the diaphragm. The right group of nodes, which are juxtaposed to the pericardium and the distal part of the intrathoracic inferior vena cava, drain the central diaphragm and the convex surface of the liver. They subsequently drain to the parasternal, posterior mediastinal and brachiocephalic lymph nodes.
• The posterior group of diaphragmatic nodes will be discussed below with the nodes of the posterolateral thoracic wall.

Intercostal lymph nodes

The intercostal lymph nodes have the responsibility of draining the posterolateral chest. They can be found at the costovertebral junction along the thoracic vertebrae. The efferent vessels of the nodes of the caudal four to seven intercostal spaces anastomose to form a single trunk that travels inferiorly and inserts into the proximal part of the thoracic duct. Efferent lymphatics of node of the cranial left and right intercostal spaces drain to the thoracic duct and right lymph trunks, respectively.

Posterior thoracic diaphragmatic group of nodes are found on the posterior surface of the diaphragmatic crura. They form a communication between the posterior mediastinal and lateral aortic nodes.

Thoracic duct

The thoracic duct and right lymphatic duct are two major lymph channels found close to the posterior thoracic wall.

The thoracic duct commences at the L1/L2 level, anterior and slightly to the right of the vertebral bodies and travels about 38 to 45 cm to the base of the neck in adults. The vessel is wider at its origin, where the lumbar lymph trunks unite. Occasionally, there is a lymphatic cistern (a swelling or waterproof receptacle) known as the cisterna chyli.

The thoracic duct becomes narrower as it moves cranially before dilating again prior to terminating in the jugulo-subclavian junction. The thoracic duct contains several valves at high pressure points where some tributaries join the vessel to prevent the reflux of lymph. The thoracic duct travels adjacent to the azygous and hemiazygous veins, and the aorta in the retrocrural part of the diaphragm.

It continues to the right of the midline of the thoracic cavity through the posterior mediastinum, with the thoracic aorta to its left and the azygous vein on the right. Posteriorly related structures include the vertebral column, terminal hemiazygous and accessory hemiazygous veins, and the right intercostal arteries; while anteriorly related structures include the diaphragm and oesophagus.

The fifth thoracic vertebra marks the point at which the thoracic duct courses towards the left as it enters the superior mediastinum, before progressing towards the thoracic inlet. It is noteworthy that at this point the thoracic aorta is located to the right of the duct.

At the seventh cervical vertebra, it curves laterally, after which it courses posterior to the left common carotid artery, internal jugular vein and vagus nerve (CN X) before descending towards and terminating in the jugulo-subclavian junction. It is not uncommon for the duct to terminate in either the subclavian or internal jugular veins, rather than the junction of the two. As previously mentioned, there are several tributaries to the thoracic duct. These include:

• Bilateral vessels from the intercostal lymph nodes of the caudal 6 – 7 intercostal spaces descending to join the duct. 
• Bilateral lumbar lymph vessels travelling cranially from the superior aortic nodes to anastomose and form the thoracic duct. 
• Efferents from the cranial 5 – 6 intercostal nodes on the left hand side. 
• Mediastinal nodes from a myriad of nodal groups. 
• The left jugular trunk and left bronchomediastinal trunk on occasion drain into the thoracic duct, but may also drain into their respective independent venous openings.

Right lymphatic duct

The right lymphatic duct has several anatomical presentations including unilateral or bilateral termination, duplicate ducts or left-sided termination. It is approximately 1.25 cm long and travels on the medial edge of scalenus anterior. The vessel then terminates in the right jugulo-subclavian junction. Like the thoracic duct, the right lymphatic duct also has semilunar valves at its opening to prevent the reflux of lymphatic fluid. Afferents to this vessel arise from the right jugular and subclavian trunks as well as from the right upper limb (lateral group of axillary nodes). The right side of the heart, right lung, and the right sides of the head, neck and thorax also drain into the right lymphatic trunk.

Cancer

One of the main clinical reasons for appreciating lymph node location is to accurately stage metastasis of cancer.

Cancer cells can spread via the lymphatic system and subsequently result in secondary malignancies. It isn’t uncommon, for example, for gastroenteric carcinomas to spread to the lungs because their common lymphatic channels. The mediastinal nodes, in particular, have been arranged into stations in order to better appreciate the staging of lung cancer. While there are no clear-cut demarcations signifying transition points between stations, the approximation assists in assessing cancer staging:

• Station 1 nodes are superior to the horizontal line that marks the point at which the left brachiocephalic vein crosses the trachea;
• Station 2 nodes are inferior to the line of the uppermost mediastinal nodes, but inferior to the horizontal landmark at the upper border of the aortic arch. These are known as the paratracheal nodes;
• Station 3 nodes are prevascular and retrotracheal nodes that are anterior to the great vessels but posterior to the trachea;
• Station 4 nodes are the inferior paratracheal group of nodes found caudal to the superior border of the aortic arch and cranial to the border of the upper lobe bronchi bilaterally. The nodes are typically seen anterolateral to the trachea with the ligamentum arteriosum located laterally.
• The subaortic nodes are found in station 5. They are found lateral to the ligamentum arteriosum or left pulmonary artery and near the proximal end of the first part of the left pulmonary artery.
• Station 6 nodes reside lateral to the aortic arch and ascending aorta and caudal to the superior margin of the aortic arch. They are collectively known as the para-aortic nodes.
• Station 7 nodes are situated below the bifurcation of the trachea; a point known as the carina. Conveniently, the nodes are known as the subcarinal nodes and they have no association with the lower lobe bronchi.
• Para-oesophageal nodes distal to the carina and found bilateral to the thoracic oesophagus are found at station 8.
• Finally, nodes of the pulmonary ligament are called station 9.

Anatomic variation of the thoracic duct

Throughout nature there are several anatomical variations among members of the same species. The thoracic duct is no exception to this phenomenon, as there are differences in the course it travels in the thoracic cavity. The most common variant of the thoracic duct (60 - 65%), as described above, shows the duct commencing at L2 and traveling cranially. It then decussates at the level of T4 and continues cranially to the left of the vertebral column until it terminates at the jugulo-subclavian junction.

In some cases, the thoracic duct does not decussate at all. It travels on the side of origin (4% incidence on the left and 4% incidence on the right) and drains into the ipsilateral jugulo-subclavian venous system. About 15 - 20 % of individuals may have duplicated ducts distally that coalesce on the left-hand side before draining into the left jugulo-subclavian system. Another 12 - 15% of individuals have paired thoracic ducts that travel adjacent to the thoracic aorta in a cranial manner; each vessel subsequently drains to the ipsilateral jugulo-subclavian venous systems.

Chyle fistula

The walls of the lymphatic vessels are less robust than those of arteries and veins. As a result, they can be easily damaged iatrogenically/inadvertently or otherwise. Injury to the lymph vessels may also result in the formation of chyle fistulas. A fistula is an abnormal communication between two epithelialized surfaces (e.g. tracheoesophageal fistula, perianal fistula, etc.)

With chyle fistulas, the lymphatic fluid leaves the vessels and accumulates in the surrounding cavities. In the abdomen, this condition is referred to as a chyloperitoneum; and in the thoracic cavity, it is called a chylothorax.

Although damage to the thoracic duct is a rare occurrence, it is associated with a relatively high mortality rate. Depending on the aetiology of the chylothorax, patients may present with shortness of breath.

On examination, it is likely to find decreased tactile vocal fremitus, dull percussion note and reduced chest expansion on the affected side. Depending on the severity of the chylothorax, the physician may also not muffled heart sounds and tracheal deviation as well as displacement of the apex beat away from the affected side (mediastinal shift).